1. Field of the Invention
The present invention relates to a ferroelectric random access memory (FeRAM), and more particularly to an FeRAM which can embody a high integration cell by improving a plate line structure of a cell array block in a semiconductor memory device.
2. Description of the Background Art
In general, an FeRAM has a data processing speed equivalent to a dynamic random access memory (DRAM), preserves data even when power is off, and thus gains popularity as a next generation memory.
The FeRAM is a memory having an extremely-similar structure to the DRAM. The FeRAM employs a ferroelectric substance to form capacitors, and thus uses high remanent polarization which is a property of the ferroelectric substance. Even if electric fields are removed, data are not deleted in the FeRAM due to the remanent polarization.
The technical descriptions of the FeRAM have been disclosed in Korea Patent application No. 2002-85533 by the same inventors as the present invention. Therefore, detailed explanations of the basic structure and operation principles of the FeRAM are omitted.
As a design rule of a semiconductor memory device decreases, a size of an FeRAM cell gradually decreases. When different plate lines are used in each row of a cell array, a cell area is not reduced. Especially in the case of a three-dimensional cell, it is much more difficult to distinguish plate lines by cell arrays. Accordingly, high integration of the cell is not achieved.
In addition, when the plate lines are etched in the FeRAM, a ferroelectric substance is exposed to plasma atmosphere, and thus a ferroelectric film is deteriorated by plasma damages. Therefore, the FeRAM is not efficiently crystallized, and properties thereof become inhomogeneous according to cell distribution in the cell array.